I don't know if it's a translation thing because English isn't my first language but I mean myth as in part or all of the story of origins of the world as a whole as well as of certain aspects of it, central or very important to a belief system or something like that.I have stated before that we need to be very careful when we use the word 'myth', we are not using the modern meaning as "Something that is believed, but not true." Tolkien would have wholeheartedly rejected that. To him, myth was just as true as anything else. I don't think we have to be afraid to show the world as described in the Ainulindale, and have it seem "too real", because to Tolkien, myth is real. (Was, but you get my point.)
The "too real" thing - well I'm not sure I agree. But I'm not sure it's a problem. Tolkien doesn't describe the Halls with a lot of detail, so we don't have to either.